1-phenylazo-2-naphthol

Endpoint summary

Description of key information

Short term toxicity to fish

A study was predicted using OECD QSAR toolbox version 3.3 (2017); to assess the toxicity effect of 1-phenylazo-2-naphthol on fish in a 96 hours of exposure. The median lethal concentration (LC50) for the test substance, 1-phenylazo-2-naphthol, in Danio rerio on the basis of mortality effect was estimated to be 366.43 mg/L. Thus, on the basis of this LC50 value and according to CLP Criteria for aquatic classification of the substance, it is concluded that 1-phenylazo- 2-naphthol (CAS no. 842 -07 -9) does not exhibit short term toxicity to fish.

Short term toxicity to aquatic invertebrates

Determination of the acute effect on the swimming ability of the Daphnia magna straus was performed using OECD guideline 202. Limit test was conducted at 100 mg/l concentrations. The test substance was suspended in water. The daphnids were exposed to various concentrations of the test substance and compared to a control. Synthetic fresh water was used for culture and test purposes. M4 medium was used and aerated for approximately 24 h until saturation with oxygen is reached. Proper test conditions were maintained. No feeding during test was done. Measurement of temperature continuously during the whole test period in a separate vessel close the test vessels and measurement of pH and oxygen after 0h in an additional replicate without daphnids and after 48h in replicate 1 of each tested concentration were taken.The test substance was stirred in M4 medium for about 20 hours at 20 ± 2°C. Undissolved test substance was removed by filtration with a membrane filter. The test is fulfilled the validity criteria.

From the experiment, it can be seen that, the EC 50 value for1-phenylazo-2-naphthol (Sudan Orange 220) (CAS No.842-07-9)for daphnia magna was determined to be >100mg/l.

Based on result, the1-phenylazo-2-naphthol (Sudan Orange 220) (CAS No.842-07-9)was considered to be non toxic to aquatic invertebrates and considered to be not classified as per the CLP regulation.

Toxicity to aquatic algae and cyanobacteria

The freshwater algal growth inhibition test was carried out on Desmodesmus subspicatus with the substance 1-phenylazo-2-naphthol (CAS No.- 842-07-9) according to OECD Guideline 201. The median effective concentration (EC50) for the test substance, 1-phenylazo-2-naphthol, in a freshwater algae Desmodesmus subspicatus was determined to be 41.8 mg/L on the basis of effects on growth rate in a 72 hour study with 95% CL of 18.8 - 92.6 mg/L and also the substance was found to be not rapidly degradable. Thus considering the CLP criteria for aquatic classification of the substance, it is concluded that the substance ‘1-phenylazo-2-naphthol (CAS No. 842-07-9)’ exhibits toxicity to aquatic algae in the chronic 3 classification category.

Toxicity to microorganisms

The Inhibition of Oxygen Consumption by Activated Sludge in the Activated Sludge Respiration Inhibition Test according to OECD Guideline 209 was determined for 1-phenylazo-2-naphthol (Sudan Orange 220). Based on the experiment the EC20, EC50 and EC80 was reported as >1000 mg/L in a 180 min. of exposure period on the basis of inhibition of oxygen consumption effect.

Additional information

Short term toxicity to fish

Various studies including experimental data and predicted results from validated model for toxicity to aquatic fish with the target substance 1-phenylazo-2- naphthol (CAS No. 842-07-9) and to its relevant read across substance 9-(2-carboxyphenyl)-3,6-bis(diethylamino)xanthylium chloride (CAS No.- 81-88-9) by considering its structure-activity relationships, were summarized as follows: 

  

A study was predicted using OECD QSAR toolbox version 3.3 (2017); to assess the toxicity effect of 1-phenylazo-2-naphthol on fish in a 96 hours of exposure. The median lethal concentration (LC50) for the test substance, 1-phenylazo-2-naphthol, in Danio rerio on the basis of mortality effect was estimated to be 366.43 mg/L.

 

Moreover, in a study conducted by Marking,L.L. (Prog. Fish-Cult.31(3): 139-142, 1969),to assess the toxic effects of the test compound 9-(2-carboxyphenyl)-3, 6-bis(diethylamino)xanthylium chloride on the Lepomis macrochirus (Bluegill) in a 96 hours of exposure. The lethal concentrations (LC50) for the test substance, 9-(2-carboxyphenyl)-3,6-bis(diethylamino)xanthylium chloride, in fish (Lepomis macrochirus) on a mortality effect was observed to be 379 (260 - 554) mg/L.

 

So, based on the above predicted and experimental studies for target substance 1-phenylazo- 2-naphthol (CAS no. 842 -07 -9) and to its read across substance, the lethal concentration LC50 value was found to be in the range of 366.43 mg/L to 379 mg/L. Thus, on the basis of this LC50 value and according to CLP Criteria for aquatic classification of the substance, it is concluded that 1-phenylazo- 2-naphthol (CAS no. 842 -07 -9) does not exhibit short term toxicity to fish.

Although this value suggests that the substance is not classified in short term toxicity to fish, since it is classified in Aquatic chronic category 4 as per the Harmonised classification - Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation), the same has been considered for the dossier.

Short term toxicity to aquatic invertebrates

Various experimental studies for toxicity toaquatic invertebratewith the target substance 1-phenylazo-2-naphthol (CAS No. 842-07-9) were summarized as follows:

In the first experimental study conducted by BASF () determination of the acute effect on the swimming ability of the Daphnia magna straus was performed using OECD guideline 202. Limit test was conducted at 100 mg/l concentrations. The test substance was suspended in water. The daphnids were exposed to various concentrations of the test substance and compared to a control. Synthetic fresh water was used for culture and test purposes. M4 medium was used and aerated for approximately 24 h until saturation with oxygen is reached. Proper test conditions were maintained. No feeding during test was done. Measurement of temperature continuously during the whole test period in a separate vessel close the test vessels and measurement of pH and oxygen after 0h in an additional replicate without daphnids and after 48h in replicate 1 of each tested concentration were taken.The test substance was stirred in M4 medium for about 20 hours at 20 ± 2°C. Undissolved test substance was removed by filtration with a membrane filter. The test is fulfilled the validity criteria.

From the experiment, it can be seen that, the EC 50 value for 1-phenylazo-2-naphthol (Sudan Orange 220) (CAS No.842-07-9) for daphnia magna was determined to be >100mg/l. Based on result, the 1-phenylazo-2-naphthol (Sudan Orange 220) (CAS No.842-07-9) was considered to be non toxic to aquatic invertebrates and considered to be not classified as per the CLP regulation.

 

Moreover, in the second experimental study conducted by SSS (2017), determination of the inhibition of the mobility of daphnids was carried out with the substance 1-phenylazo-2-naphthol according to OECD Guideline 202. A limit test at sample concentration of 10.0 mg/L was performed. Effects on immobilisation were observed for 48 hours. The test was performed under static conditions in a fresh water system at a temperature of 20 °C ± 1 °C. EC50 was calculated. The median effective concentration (EC50) for the test substance, 1-phenylazo-2-naphthol, in Daphnia magna was determined to be >10.0 mg/L for immobilisation effects.

Although the second experimental study result indicates that the median effective concentration (EC50) to be >10.0 mg/L for immobilisation effects. The classification is not possible since the data is not conclusive based on the classification criteria mentioned in CLP regulation ( 48 hr EC 50 (for crustacea) = >10 to ≤100 mg/L). Thus, based on the first experimental study (Key study), the substance 1-phenylazo-2-naphthol (Sudan Orange 220) (CAS No.842-07-9) was considered to be non-toxic to aquatic invertebrates and considered to be not classified as per the CLP regulation.

Although based on the first experimental study (Key study), the substance 1-phenylazo-2-naphthol (Sudan Orange 220) (CAS No.842-07-9) was considered to be non-toxic to aquatic invertebrates and considered to be not classified as per the CLP regulation, since it is classified in Aquatic chronic category 4 as per the Harmonised classification - Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation), the same has been considered for the dossier.

Toxicity to aquatic algae and cyanobacteria

Various studies including experimental data following OECD guideline and predicted results from validated model for toxicity to aquatic algae with the target substance 1-phenylazo-2-naphthol (CAS No. 842-07-9) were summarized as follows:

The freshwater algal growth inhibition test was carried out by SSS (2017) on Desmodesmus subspicatus with the substance 1-phenylazo-2-naphthol (CAS No.- 842-07-9) according to OECD Guideline 201. 

The stock solution 1.0 g/L was prepared by dissolving dark reddish-orange powder in acetone. Test solutions of required concentrations were prepared by mixing the stock solution of the test sample with OECD growth medium and inoculum culture and tested at the concentrations 0, 0, 0.6, 1.2, 2.5, 5.0, 10.0 mg/L. Effects on the growth rate of the organism were studied. The test was performed under static conditions in a static fresh water system at a temperature of 23± 2°C. Initial cell density of test organism used was 9.8x10(3) cells/ml. Determination of cell counting involve the use of electronic particle counter. ErC50 was calculated using non-linear regression by the software Prism 4.0.

The median effective concentration (EC50) for the test substance, 1-phenylazo-2-naphthol, in a freshwater algae Desmodesmus subspicatus was determined to be 41.8 mg/L on the basis of effects on growth rate in a 72 hour study with 95% CL of 18.8 - 92 .6 mg/L and also the substance was found to be not rapidly degradable.

Moreover, another study was predicted using OECD QSAR toolbox version 3.4 (2017) with respect to the descriptor log Kow; to assess the toxicity effect of 1-phenylazo-2-naphthol in aquatic algae in a 72 hours of exposure. The median effective concentration (EC50) for the test substance, 1-phenylazo-2-naphthol, in algae (Desmodesmus subspicatus) on a growth rate effect was estimated to be 30.77 mg/L in a 72 hour study and also the substance was found to be not rapidly degradable.

Thus, based on the above experimental and predicted studies, the effective concentration (EC50) value was found to be in the range of 30.77 mg/L to 41.8 mg/L and also the substance was found to be not rapidly degradable. Thus considering the CLP criteria for aquatic classification of the substance, it is concluded that the substance ‘1-phenylazo-2-naphthol (CAS No. 842-07-9)’ exhibits toxicity to aquatic algae in the chronic 3 classification category.

Although this value suggests classification of the substance in Aquatic chronic category 3, since it is classified in Aquatic chronic category 4 as per the Harmoni sed classification - Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation), the same has been considered for the dossier.

Toxicity to microorganisms

The Inhibition of Oxygen Consumption by Activated Sludge in the Activated Sludge Respiration Inhibition Test according to OECD Guideline 209 was determined for 1-phenylazo-2-naphthol (Sudan Orange 220).

This test specifies a method for assessing the inhibitory effect of a test substance on the oxygen consumption rate of aerobic micro-organisms (activated sludge) after short-term exposure (30 or 180 min). The test results are reported as effective concentrations which indicate a respiration inhibition of 20, 50, and 80 % (EC20,EC50, EC80) compared to a control assay without test substance . The EC20 is regarded as a limit value for possible toxic effects in wastewater treatment plants . The test concentration in biodegradation tests should not exceed the EC20.The EC-values are based on added nominal concentrations and not on analytically determined values . The nominal concentrations which indicate a respiration inhibition of 20, 50 and 80 % can be taken from the graph of the inhibition curve.

The EC20 in the activated sludge respiration inhibition test is >100 mg/l . Disturbances in the biodegradation process of activated sludge are not to be expected if the test substance is correctly introduced into adapted wastewater treatment plants at low concentrations.

Thus, based on the experiment the EC20, EC50 and EC80 was reported as >1000 mg/L in a 180 min. of exposure period on the basis of inhibition of oxygen consumption effect.

Although based on the available data the substance is classified in Aquatic chronic category 3, though as per the Harmonised classification - Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation) the substance is classified in Aquatic chronic category 4, and the same has been considered for the dossier.